The two V nickels I've dug with the EQ800 have both rung up identically, varying uniformly between 12-13 as I swung over each one. I dug them both on the same day, just a few feet apart! Unmistakably coin-like signal in each case - the first one I strongly suspected it was a nickel...the second one, I knew for sure
I have a crusty Shield Nickel that I air tested, and it also rings up as a smooth 12-13 VDI.
War nickels seem to vary, not just with the Equinox, but other makes and models of detectors as well. Most seem to ring up like regular nickels (13 or so), but every now and then, one rings up in the silver range. I've only dug one War nickel in the field with the Equinox, and it rung up as a solid 20. Air testing the other War nickels I've found, they are all solid 13 on the VDI while air testing the one oddball still reads a solid 20. Perhaps it's a variation in the silver content for some of the War nickels?? The one that rings up high is a 1945P, but I have another 1945P that rings up 13, so it doesn't seem associated with a particular year or mint.
The few modern nickels I've dug with the EQ have all been pretty solid at 13, although I think I remember occasional blips down to 12 as I swung.
All that said, I'm sure your results are going to depend on a whole slew of variables: soil type and mineralization, moisture conditions, target depth, individual detector construction, etc will likely all play a role in what VDI shows up for nickels, and any other target for that matter!